<select v-model="flightType">
  <option value="one-way flight">One-way Flight</option>
  <option value="return flight">Return Flight</option>
</select>

<input type="date" v-model="departureDate" />
<input type="date" v-model="returnDate" :disabled="!isReturn" />

<button :disabled="!canBook" @click="book">Book</button>

<p>{{ canBook ? '' : 'Return date must be after departure date.' }}</p>
